Quote
Those fortunate enough to have D.C. mains, it explains, can charge their accumulators by unscrewing the cap from a light switch and connecting the accumulator across the terminals so that the light acts to limit the charging current.

And how do you determine the polarity of the switch terminals? Why, you take two pieces of wire, drop them into a beaker filled with a vinegar solution, and observe from which conductor the bubbles rise.

I saw similar advice in a book of similar vintage, but this one involved a 5 amp plug and socket in series with the 5 amp lighting circuit main, and a car battery. Apparently 'the reduction in voltage to your lamps will be insignificant and will actually reduce your lighting bill'.

Mention was also made of the vinegar water polarity test, with salt water not recommended as a test as both electrodes will bubble.

A stern warning was made not to attempt this if you had AC mains.

A 'shorting plug' should be provided to allow normal usage of the lighting with no battery connected, and connections to the battery should be made before connecting the plug.

No mention was made of the effects of interupting ~5amps DC around the hydrogen/oxygen buildup that would have been present in the 'cupboard under the stairs' at the time. It was probably assumed that anyone attempting this would have knowledge of this danger.

A more innocent time, for sure. (No mention of part P was made either Paul [Linked Image] )